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Fireclay - Forno Bravo Forum: The Wood-Fired Oven Community

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New Forno Bravo Forum Feature

Forno Bravo Forum Community,

You will notice a new forum at the top of the main page called, "Ask Me Anything". This forum will be used for live one hour "Ask Me Anything" (AMA) sessions hosted by people who are knowledgeable in different areas pertaining to wood fired ovens. How it works:
- Each AMA will have a "sticky" thread where the community can post questions they would like answered during the live session. This will allow everyone to participate even if you can't be online for the live session. These questions will not be answered by the host until the live AMA; if you need an answer quickly, you should post it in the appropriate Forum area for the community to respond.
- Another thread will be posted for the live AMA. Registered users who are logged in during the live session can interact with the host by asking questions and receiving responses.
- The live thread will remain in the AMA forum to view after the session.

To kick off our AMA feature, we have invited author, chef and master bread maker and host of Pizza Quest, Peter Reinhart, to be our first host! Peter will be in the Forum on Monday, February 15th, from 7:00 - 8:00 pm EST. If you are unable to be online during the live session, you can post your questions in the sticky post. Peter will answer those questions during the live session on February 15th. You can view Peter's answers to your questions as well as what happened during the live session in the session thread.

We hope you enjoy this new feature! Please let us know if there is a topic that you'd like to have as an AMA and we'll look for a host!

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Fireclay

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  • Fireclay

    I am reading up on different sites and getting all different types of info regarding what to use to set the bricks. Is the mix on this site of Sand, Portland and Fireclay strong enough to withstand the heat? some sites mention that portland breaks down at 400 degrees. Also some sites mention to add lime to the mixture which takes over when it gets real hot. Does anyone have any info or first hand expierience with using just the sand, portland, fireclay mix.

  • #2
    Originally posted by njsicilian
    I am reading up on different sites and getting all different types of info regarding what to use to set the bricks. Is the mix on this site of Sand, Portland and Fireclay strong enough to withstand the heat? some sites mention that portland breaks down at 400 degrees. Also some sites mention to add lime to the mixture which takes over when it gets real hot. Does anyone have any info or first hand expierience with using just the sand, portland, fireclay mix.
    A lot of builders have successfully used just this mixture. It is subject to some cracking, but the inherent stability of the dome structure has prevented any failures. Portland cement is unstable at firing temperatures, but the theory is that only the first inch or so is subject to temperatures above the safe limit, and even in the close to the fire section the fire clay will keep the mortar from disintegrating.

    As for me, I wanted to have an oven with close enough joints that I could use the expensive refractory mortar for all joints, and thus I designed the geodesic variant on the pompeii oven, which hasn't been completed yet, but I have great hopes for.

    I think the official line is that for home ovens which are fired occasionally, the fireclay mixture is fine, but for commercial ovens which are used continually, only refractory mortar will do.
    My geodesic oven project: part 1, part 2

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    • #3
      fireclay

      thanks for your answer. Should i build a thick layer of the motar mix over the oven dome or will that make it worse?

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      • #4
        Originally posted by njsicilian
        thanks for your answer. Should i build a thick layer of the motar mix over the oven dome or will that make it worse?
        That's what I did. When I was done setting the bricks, I smeared mortar over the outside and covered everything. I think that's what a lot of people do.

        See the threads on oven curing to find out more about cracking, etc.
        There is nothing quite so satisfying as drinking a cold beer, while tending a hot fire, in an oven that you built yourself, and making the best pizza that your friends have ever had.

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        • #5
          These all sound right to me. The fireclay provides some heat resistance to the mix. It's true that portland based concrete does not withstand heat cycling -- the main problem is the heat cycle, with expansion and contraction, that leads to breakdown. I've talked with a handful of folks who are experienced with concrete, and they say that is more a problem than just high heat itself.

          With a home oven, this isn't a huge problem. Your oven won't be fired often enough to where the mortar will be a problem. Also, the oven design is based on tight brick edges, where little mortar is exposed to the inside of the oven, where it is really hot.

          Having said all of this, we recommend true refractory mortar for our Forno Bravo ovens, and most of our customers use Refrax -- a true refractory mortar that we make. It's easier to do this with a precast oven, because there are fewer joints compared with a brick oven -- so the cost of the mortar really doesn't add up.

          There are definitely shades of grey here, but again, there are many ovens out there (including one of mine) made with the portland, sand, fireclay mix that are working and lasting just fine.

          On the oven coating, I think you are looking for a thin layer to provide some structural strength to the dome -- that's all. You definitely do not need more mass than a half brick facing out.

          James
          Pizza Ovens
          Outdoor Fireplaces

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          • #6
            thanks

            Thank you all for the info i was getting a little lost a one point but now i can move on.

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